This chapter provides an overview of what is known about cancer and severe mental disorders (SMD), like schizophrenia, bipolar disorders, and severe depressive disorders. Individuals with SMD face a significantly higher risk of early mortality, primarily driven by deteriorating physical health, chronic illnesses, multimorbidity, and preventable infections. Although cancer incidence in those with SMD is similar to the general population, their survival rates, particularly among those with schizophrenia, show a 50% increased risk of succumbing to cancer, notably for breast, lung, and colon cancers. The complex link between mental health and cancer risk varies based on specific disorders, lifestyle, genetics, and healthcare access. Research suggests potential shared genetic factors, immune system dysregulation, and biological pathways linking SMD and cancer, warranting further investigation to enhance cancer prevention and treatment strategies for individuals with SMD. People with SMD often receive advanced-stage cancer diagnoses due to neglect of physical health, low participation in cancer screening, societal stigma, and healthcare access challenges. Addressing these disparities in cancer care for individuals with SMD requires an integrated approach considering patient-related factors (e.g., awareness, stigma, lifestyle), physician-related factors (including stigma and communication difficulties), and healthcare system factors (fragmented care and limited mental health resources). Cancer screening programs for the most prevalent cancers should be tailored and targeted specifically to the SMD population. Eliminating these barriers is vital for equitable cancer care.